1. Field of the Invention
This invention relates to a dust discharging method and system, more particularly to a flue dust discharging method and system for a blast furnace that can prevent escape of flue gas into the atmosphere and that can minimize the cost of recycling the flue dust.
2. Description of the Related Art
Referring to FIG. 1, a conventional flue dust discharging system includes a dust collector 81 which collects flue dust 801 from flue gas produced from a blast furnace (not shown) and which has a discharge opening 811, a discharge conduit 82 connected to and disposed below the dust collector 81 and communicated with the discharge opening 811, an upper gate valve 821 and a lower gate valve 822 disposed apart from each other on the discharge conduit 82 to control discharge of the flue dust 801, a damper 823 disposed on the conduit 82 between the upper and lower gate valves 821, 822 to control a discharge speed, a screw conveyor 83 connected to and disposed below the discharge conduit 82 and receiving the flue dust 801 that is associated with residual flue gas 802 and that is discharged from the discharge conduit 82, and a sprinkler 84 to sprinkle water into the screw conveyor 83. The screw conveyor 83 has two rotatable screw rods (not shown), and is connected with a discharge tube 831 for discharging the moistened flue dust 801 therethrough.
When the dry flue dust 801 passes through the discharge conduit 82 and falls into the screw conveyor 83, and a suitable amount of water is sprinkled into the screw conveyor 83, the flue dust 801 is mixed with the water through the screw rods in the screw conveyor 83. The moistened flue dust 801 is then pushed down the discharge tube 831 into an open-type receptacle 851, which is disposed below the discharge tube 831, of a loading truck 85. During discharging, the hazardous residual flue gas 802 is prevented from escaping into the atmosphere by the moistened furnace dust 801 which can act as an obstruction in the screw conveyor 83.
However, during the discharging operation, the typical temperature of the flue dust 801 accumulated in the dust collector 81 is about 150° C., so that when the flue dust 801 is mixed with water in the screw conveyor 83, a large amount of steam is produced. Further, if the moistness of the flue dust 801 is not uniform, when the flue dust 801 is discharged into the open-type receptacle 851 of the loading truck 85, the dry portion of the flue dust 801 may become scattering in air and thereby pollute the environment of the workplace. Moreover, because the receptacle 851 of the loading truck 85 is open, during transport and unloading of the flue dust 801 to a storage area, a large amount of steam escapes and the dry flue dust 801 becomes scattering in air, thereby polluting and damaging the environment of the workplace. The safety of workers is also endangered.
Additionally, many manufacturers recycle the flue dust 801 by subjecting the flue dust 801 to a pelletizing operation, so that the flue dust 801 can be fed into the blast furnace again, there by minimizing the cost of feed material. However, the flue dust 801 must be dry in order to perform pelletizing, and the discharged moistened flue dust 801 of the conventional dust discharging system, which has a moisture content of about 13%, must first undergo a drying operation. Hence, the cost of recycling the flue dust 801 is increased.